The IRS normally has three years to audit a return and assess more tax, but the six-year statute of limitations kicks in when you leave off more than 25 percent of the gross income that should have appeared on that return. The rule lives in Internal Revenue Code Section 6501(e), and it applies whether the omission was a careless mistake or something worse.1Office of the Law Revision Counsel. 26 USC 6501 – Limitations on Assessment and Collection A separate trigger, discussed further down, applies a much lower threshold to foreign income.
What Triggers the Six-Year Window
The test compares what you left off your return to what you reported on it. If the omitted gross income exceeds 25 percent of the gross income shown on the return, the IRS gets six years instead of three. So a return showing $100,000 of gross income and missing another $30,000 crosses the line; the gap is more than a quarter of what you reported.
Intent is not part of this calculation. An honest arithmetic error that clears 25 percent triggers the same extension as a deliberate scheme.2Internal Revenue Service. Time IRS Can Assess Tax The statute talks about a “substantial omission of items,” which is a different concept from the “substantial understatement” penalty that appears elsewhere in the code. People routinely mix them up. The six-year rule is about how long the IRS has to come after you; the understatement penalty is about how much extra you owe when it does.
How Gross Income Is Measured for the Test
The denominator in the 25 percent calculation depends on what kind of income you have, and the definition is not always intuitive.
For wages, interest, dividends, rental income, and capital gains, gross income means the full amount received from all sources before any deductions or exemptions.3Office of the Law Revision Counsel. 26 USC 61 – Gross Income Defined
For a trade or business, gross income means total receipts from selling goods or services before subtracting the cost of those goods or services.4Office of the Law Revision Counsel. 26 US Code 6501 – Limitations on Assessment and Collection A retailer with $500,000 in sales and $350,000 in cost of goods sold uses $500,000 as the denominator, not $150,000. That top-line measurement stops businesses from shrinking their reported gross income by loading up expenses.
For property sold outside a trade or business, gross income is the profit on the sale: the sale price minus your basis.5Federal Register. Definition of Omission From Gross Income That distinction changes the denominator and can push borderline cases over or under the 25 percent line.
Overstated Basis Now Counts as an Omission
For years, inflating the cost basis of property you sold looked like a way to shrink your reported gain without technically omitting anything. The Supreme Court agreed with that reading in 2012 in United States v. Home Concrete & Supply, LLC, holding that an overstatement of basis was not an omission from gross income.6Justia Law. United States v. Home Concrete and Supply LLC, 566 US 478 (2012)
Congress reversed that result in 2015. Under the current statute, understating gross income because you overstated basis is an omission for purposes of the six-year rule.1Office of the Law Revision Counsel. 26 USC 6501 – Limitations on Assessment and Collection So if you sell stock or real estate and claim a higher purchase price than you actually paid, the resulting underreported gain feeds into the 25 percent calculation. The change applied to returns filed after July 31, 2015, and to any return still open on that date.
One trap worth knowing: the disclosure escape hatch described below does not save a basis overstatement. Even a detailed attachment explaining your numbers will not shut off the six-year period if the overstated basis pushes you over 25 percent.
Disclosing an Item to Keep the Three-Year Rule
For omissions other than basis overstatements, you can prevent the extension by adequately disclosing the item on your return. The statute says the item is not treated as omitted if you disclose it, or attach a statement, with enough detail for the IRS to identify the nature and amount involved.1Office of the Law Revision Counsel. 26 USC 6501 – Limitations on Assessment and Collection The logic: if you flagged it, the IRS had a fair chance to look at it within three years.
The usual vehicle is Form 8275 (Disclosure Statement), which lets you describe the facts, the amount, and how you treated the item. A related form, Form 8275-R, is used when your position directly contradicts a Treasury regulation, and it requires that your position have a reasonable basis and represent a good-faith challenge to the regulation.7Internal Revenue Service. Instructions for Form 8275-R, Regulation Disclosure Statement Both forms can also help avoid accuracy-related penalties, so disclosure has value beyond preserving the shorter statute.
Foreign Income Has a Much Lower Threshold
The same statute contains a separate six-year trigger for foreign income, and it bites at a far lower amount. Omit more than $5,000 of gross income tied to assets that would be reportable under FATCA, and the IRS gets six years regardless of whether the omission is anywhere near 25 percent of your total reported income.4Office of the Law Revision Counsel. 26 US Code 6501 – Limitations on Assessment and Collection
Covered assets include foreign bank accounts, foreign stocks and securities, interests in foreign entities, and financial instruments held through foreign institutions. These are the assets generally reportable on Form 8938 when their combined value exceeds certain thresholds. For taxpayers living in the United States, the Form 8938 filing threshold is $50,000 at year-end or $75,000 at any point during the year for single filers, and $100,000 at year-end or $150,000 at any point for married couples filing jointly. Those numbers roughly double for taxpayers living abroad.8Internal Revenue Service. Do I Need to File Form 8938, Statement of Specified Foreign Financial Assets
Missing Foreign Forms Can Keep Your Return Open Forever
A separate provision is harsher than the six-year rule. Under IRC 6501(c)(8), the assessment clock does not start at all until you file certain required foreign information returns.9Internal Revenue Service. Overview of Statute of Limitations on the Assessment of Tax If you never file Form 5471 (interests in foreign corporations), Form 3520 (transactions with foreign trusts), Form 8865 (foreign partnerships), or Form 8938, the year stays open indefinitely. Once you do file, you get three years from that point.
If your failure to file was due to reasonable cause and not willful neglect, the IRS’s reach is limited to items tied to the unreported foreign information rather than the entire return. Reasonable cause is a high bar, and simply not knowing the forms existed often does not meet it.
When the Clock Starts and How It Can Be Extended
The assessment period runs from the later of the date you filed the return or the return’s due date.2Internal Revenue Service. Time IRS Can Assess Tax Filing early does not start the clock early; a return submitted February 15 for an April 15 deadline is treated as filed on April 15. Filing late without an extension starts the clock on the actual filing date.
An amended return generally does not restart the clock. There is one narrow wrinkle: if the IRS receives a signed amended return within the last 60 days before the statute expires, the agency gets 60 additional days from receipt to assess tax on the items in that amendment.10Internal Revenue Service. Statute of Limitations Processes and Procedures Outside that sliver, an amendment does not give the IRS extra time.
The IRS can also ask you to sign a written agreement extending the assessment period, and this happens routinely during audits that are running up against the deadline. You have the right to refuse, and the IRS must tell you about that right each time it asks.11Office of the Law Revision Counsel. 26 USC 6501 – Limitations on Assessment and Collection You can also propose a shorter extension or one limited to specific issues. Refusing outright often pushes the IRS to issue a deficiency notice before it has finished its review, which tends to produce a larger proposed adjustment than a completed audit would have.
Fraud and Non-Filing Have No Statute at All
The six-year rule is the outer limit for filed returns with unintentional or negligent omissions. Three situations remove the time limit entirely, all under IRC 6501(c):4Office of the Law Revision Counsel. 26 US Code 6501 – Limitations on Assessment and Collection
- A return filed with the intent to evade tax
- A willful attempt to defeat or evade tax in any manner
- No return filed at all
The IRS carries the burden of proving fraud by clear and convincing evidence. When it meets that burden, every year involving a fraudulent return remains permanently open. That is why the line between a careless mistake and a deliberate scheme matters so much: a $30,000 omission might give the IRS six years if accidental, or forever if intentional.
What an Old Assessment Actually Costs
Tax assessed on a five- or six-year-old return rarely arrives alone. Interest runs from the original due date, compounded daily, at the federal short-term rate plus three percentage points, adjusted quarterly. The underpayment rate is 7 percent for the first quarter of 2026 and 6 percent for the second quarter.12Internal Revenue Service. Quarterly Interest Rates On a $10,000 deficiency six years out, the interest alone can add thousands.
The accuracy-related penalty adds 20 percent of the underpayment when there is a substantial understatement of tax. For individuals, that trigger is an understatement of the greater of 10 percent of the correct tax or $5,000.13Internal Revenue Service. Accuracy-Related Penalty For most corporations, the threshold is the lesser of 10 percent of correct tax (or $10,000 if greater) and $10,000,000. A Form 8275 or 8275-R disclosure of a position with reasonable basis can head off this penalty even when the IRS disagrees with your treatment.
When the IRS establishes fraud, the penalty rises to 75 percent of the underpayment attributable to fraud.14Office of the Law Revision Counsel. 26 US Code 6663 – Imposition of Fraud Penalty Once any part of the underpayment is shown to be fraudulent, the entire underpayment is presumed fraudulent unless you rebut it by a preponderance of the evidence.
Refunds Do Not Work the Same Way
The statute is not symmetrical. Even when the IRS has six years to assess more tax, you have only three years from the date you filed the return or two years from the date you paid the tax, whichever is later, to claim a refund.15Office of the Law Revision Counsel. 26 US Code 6511 – Limitations on Credit or Refund Miss that window and the overpayment is gone, no matter how clearly you can prove it. If you find an error on a five-year-old return, the IRS can still collect on an understatement of that size, but you likely cannot recover an overpayment of the same age.